全文获取类型
收费全文 | 6345篇 |
免费 | 925篇 |
国内免费 | 530篇 |
专业分类
化学 | 2228篇 |
晶体学 | 54篇 |
力学 | 185篇 |
综合类 | 54篇 |
数学 | 392篇 |
物理学 | 4887篇 |
出版年
2024年 | 19篇 |
2023年 | 82篇 |
2022年 | 158篇 |
2021年 | 173篇 |
2020年 | 205篇 |
2019年 | 171篇 |
2018年 | 160篇 |
2017年 | 168篇 |
2016年 | 249篇 |
2015年 | 211篇 |
2014年 | 228篇 |
2013年 | 394篇 |
2012年 | 290篇 |
2011年 | 360篇 |
2010年 | 286篇 |
2009年 | 376篇 |
2008年 | 423篇 |
2007年 | 465篇 |
2006年 | 407篇 |
2005年 | 307篇 |
2004年 | 312篇 |
2003年 | 335篇 |
2002年 | 320篇 |
2001年 | 251篇 |
2000年 | 266篇 |
1999年 | 175篇 |
1998年 | 179篇 |
1997年 | 113篇 |
1996年 | 67篇 |
1995年 | 82篇 |
1994年 | 64篇 |
1993年 | 57篇 |
1992年 | 55篇 |
1991年 | 37篇 |
1990年 | 46篇 |
1989年 | 34篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 33篇 |
1985年 | 28篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 22篇 |
1980年 | 18篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1974年 | 8篇 |
排序方式: 共有7800条查询结果,搜索用时 15 毫秒
52.
本文根据空心阴极放电中电子能量分布的物理图象,分析了原子从低激态向高激态弛豫的可能途径。建立高低激态集居数密度增量的关系。讨论高激态集居数密度增量获得可观量的条件。根据此条件分别选取钠原子的基态3s~2S_(1/2)和铜原子的亚稳态4s~2D_(3/2)为与激光共振的下能级,并激发具有较大自发发射几率的3s~2S_(1/2)→3p~2P°_(1/2)(和3p~2P°_(3/2))和4s~2D_(3/2)→4p~2P°_(1/2)跃迁,在远离上能级的高激态上观测到敏化荧光,并精确测得这些态的自发发射系数比值,而在更高激态上没有观测到敏化荧光,表明讨论中提出的条件是合理的。 相似文献
53.
Michael K. -H. Kiessling 《Journal of statistical physics》1990,59(5-6):1157-1186
The canonical equilibrium measure of classical two-component Coulomb matter with regularized interactions is analyzed in a finite volume. It is shown that, in the mean-field regime, the one-particle density is inhomogeneous on a new characteristic length scale inh. For a system ofN positive andN negative particles, inh and the characteristic length scale of correlations corr (=Debye screening length) are related via inh=(2N)1/2 corr. The major conceptual conclusion that is drawn from this is that one needs two nontrivial complementary thermodynamic limits to define the equilibrium thermodynamics of two-component Coulomb systems. One of them is the standard thermodynamic limit (infinite volume), where one takesN, corr fixed. Its complementary limit is characterized byN, inh fixed, and is a finite-volume inhomogeneous mean-field limit. The most prominent new feature in the mean-field thermodynamic limit, which is absent in the standard thermodynamic limit, is an anomalous first-order phase transition where the Coulomb system explodes or implodes, respectively. The phase transition is connected with the existence of a metastable plasma phase far below the ionization temperature. 相似文献
54.
We investigate the topology of the phase diagram of binary alloys on the fee lattice with first-neighbor antiferromagnetic interactions around the superdegenerate point, where the L10 and L12 phases meet. We treat the system as a hard-constraint lattice gas, following a procedure previously described by Lebowitzet al. We perform cluster variation method calculations in theT0 limit and Monte Carlo simulations directly atT=0 K on the ground states of the superdegenerate point. We find that: (i) there is no disordered phase in the neighborhood of this point; (ii) a phase L for which two of the four cubic sublattices have the same average occupancy and each of the two others are different appears between L10 and L12; (iii) the transition L/L12 is of first order. 相似文献
55.
We prove that Gibbs states for the Hamiltonian
, with thes
x varying on theN-dimensional unit sphere, obtained with nonrandom boundary conditions (in a suitable sense), are almost surely rotationally invariant if
withJ
xy i.i.d. bounded random variables with zero average, 1 in one dimension, and 2 in two dimensions. 相似文献
56.
Thomas Unnerstall 《Journal of statistical physics》1989,54(1-2):379-403
The irreversible macroscopic dynamics of the Josephson junction coupled to external wires acting as a current source is derived rigorously from the underlying microscopic Hamiltonian quantum mechanics. The external systems are treated in the singular coupling limit. The use of this limit is explicitly justified via an interpretation of the singular coupling limit in terms of the relative magnitudes of system, reservoir, and coupling energies. The qualitative behavior of the macroscopic dynamical equations is shown to depend sensitively and crucially on the interaction between the wires and the superconductors and on the size of the wires: the dc Josephson effect only happens when one lets Cooper pairs be driven into the junction by collective (i.e., small) reservoirs. 相似文献
57.
I. A. Machkarovskaya K. Ya. Burshtein V. A. Petrosyan 《Russian Chemical Bulletin》1995,44(11):2053-2059
A series ofS
N2 reactions with halomethanes as substrates and the corresponding anions as nucleophiles were studied by the semiempirical MNDO and AM1 methods, taking into account solvent effects. Analysis of the kinetics, structures of reagents, intermediates and products, and charge distribution in them allows one to draw the conclusion that the retardation ofS
N2 reactions is stronger in solvents than in the gas phase, and the rates of reactions involving anions with a lower number of halogen atoms are higher.For Part 8 see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2148–2154, November, 1995.This work was partially financially supported by the International Science Foundation (Grant No. MHYOO). 相似文献
58.
59.
60.
Gostev F. E. Petrukhin A. N. Titov A. A. Shienok A. I. Marevtsev V. S. Sarkisov O. M. 《Russian Chemical Bulletin》2003,52(3):557-561
Intramolecular processes in electronic-excited states of 2,4,5-triarylimidazole molecules were studied by femtosecond laser spectroscopy. Experiments were carried out with two types of compounds, namely, those experiencing intramolecular proton transfer and two model compounds in which it is impossible. Schemes of the processes studied were proposed and the characteristic rate constants were determined. The excited-state intramolecular proton transfer (ESIPT) in the molecules with planar structure of the reaction center is a very fast process (100 fs). If the reaction center has a nonplanar structure and, hence, the intramolecular hydrogen bond is weakened, the ESIPT time is determined by the time of conformational rearrangement of the molecule. 相似文献